Applications of Distributed Systems

a seminar about Applications of Distributed Systems for the Faculty of Information Technology Engineering in Damascus University

1. Applications of Distributed Systems Distributed systems Dr. bassem Kussayba

2. Layout Distributed Operating Systems Distributed File Systems Distributed Shared Memory Distribution Database Systems “Killer” Applications 2

3. Distributed Operating Systems 3

4. Distributed Operating Systems - Definition Not all operating systems are on a single CPU 4

5. Distributed Operating Systems – Types and Services 5

6. Distributed Operating Systems – Examples IRIX operating system DYNIX operating system AIX operating system Solaris operating system OSF/1 operating system … 6

7. Distributed Operating Systems – Goals 7

8. Distributed Operating Systems – Implementation Issues Identification/Name Resources must have unique address naming scheme such as URL Distributed Coordination Processes required to synchronization Interprocess Communication Client/server model Remote Procedure Call (RPC) Distributed Resources Fault Tolerance and Security 8

9. Distributed Operating Systems – Synchronization 9

10. Layout Distributed Operating Systems Distributed File Systems Distributed Shared Memory Distribution Database Systems “Killer” Applications 10

11. Distributed File System 11 File System Distributed File System

12. Distributed File System Architectural options Fully distributed files distributed to all sites Client-server Model Fileserver: dedicated sites storing files perform storage and retrieval operations Client: rest of the sites use servers to access files 12

13. Distributed File System – Client/Server Architecture 13

14. Distributed File System - Services 14

15. Distributed File System – Data Access in Client/Server 15

16. Distributed File System – Issues - Protection Access Failure  Replication (distributing copies of data on multiple servers)  Additional Storage in the Data Center Two related concepts Capabilities Access Control Lists Cryptographic File System 16

17. Distributed File System – Issues - Naming Approaches to naming files in a distributed system Concatenate name of host to names of files on that host Have a single global directory All files belong to a single name space Having unique system wide filenames require a single computing facility or cooperating facilities 17 Advantage Disadvantages unique filenames Conflicts with network transparency simple resolution Moving file to another host requires changing its name and the applications using it

18. Distributed File System – Issues - Caching Caching at the Client 18 Main Memory Disk + - + - Fast Expensive memory Large files Requires local disk Works for diskless clients Complex Virtual Memory Management Simpler Virtual Memory Management

19. Distributed File System – Issues - Caching   Cache consistency 19

20. Distributed File System – Issues – Writing Policy once a client writes into a file (and the local cache), when should the modified cache be sent to the server ? Write-through All writes at the clients, immediately transferred to the servers Reliability It does not take advantage of the cache Slow Performance 20

21. Distributed File System – Issues – Writing Policy once a client writes into a file (and the local cache), when should the modified cache be sent to the server ? Delayed writing Delay transfer to servers Many writes take place (including intermediate results) before a transfer Some data may be deleted No reliability 21

22. Distributed File System – Issues – Writing Policy once a client writes into a file (and the local cache), when should the modified cache be sent to the server ? Delayed writing until file is closed at client For short open intervals, same as delayed writing For long intervals, reliability problems 22

23. Distributed File System – Issues – Availability what is the level of availability of files in a distributed file system? Use replication to increase availability Many copies (replicas) of files are maintained at different sites/servers How to keep replicas consistent How to detect inconsistency among replicas 23

24. Layout Distributed Operating Systems Distributed File Systems Distributed Shared Memory Distribution Database Systems “Killer” Applications 24

25. Distributed Shared Memory A shared memory abstraction what is implemented on a loosely coupled system 25

26. Distributed Shared Memory-Stumm and Zhou's Classification Central-server algorithm Non-migrating and non-replicated Client: Sends a data request to the central server Central server: Receives the request, performs data access and sends a response Client: Receives the response Migration algorithm Migrating and non-replicated Client: If the needed data object is not local, determines the location and then sends a request. Remote host: Receives the request and then sends the object. Client: Receives the response and then accesses the data object (read and /or write) 26

27. Distributed Shared Memory-Stumm and Zhou's Classification Read-replication algorithm Migrating and replicated Client: If the needed object is not local, sends a request Remote host: Receives the request and then sends the object Client: Receives the object and then multicasts by sending either invalidate or update messages to all sites that have a copy of the data object Remote host: Receives an invalidation signal and then invalidates its local copy, or receives an update signal and then updates the local copy. Client: Accesses the data object (write ) 27

28. Distributed Shared Memory-Stumm and Zhou's Classification Full-replication algorithm Non-migrating and replicated Client: If it is a write, sends the data object to the sequencer. Sequencer: Receives the data object and adds a sequence number. Sends the client a signal with the sequence number and multicasts the data object together with the sequence number to all the other sites (Client) Receives the acknowledgment and updates local memory based on the sequence number of each data object. (Other sites) Receive the data object and update local memory based on the sequence number of each data object 28

29. Layout Distributed Operating Systems Distributed File Systems Distributed Shared Memory Distribution Database Systems “Killer” Applications 29

30. Distributed Database Systems A collection of multiple, logically interrelated databases distributed over a computer network Possible design alternatives Autonomy Distribution Heterogeneity 30

31. Distributed Database Systems - Essentials 31

32. Distributed Database Systems - Issues Network scaling problem Distributed query processing Integration with distributed operating systems Heterogeneity Concurrency control Security 32

33. Layout Distributed Operating Systems Distributed File Systems Distributed Shared Memory Distribution Database Systems “Killer” Applications 33

34. “Killer” Applications Distributed Object-based Systems CORBA Distributed Document-based Systems WWW Distributed Coordination-based Systems JINI Distributed Multimedia Systems QoS requirements Emerging Systems Wireless networks & mobile computing Grid 34

35. Presented by: Abdul Majeed Al-Kattan Rabee Al-Rass Rahaf Aamer Rimon Koroni Sandra Sukarieh 35 THANK YOU.